Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 220856

Area Forecast Discussion
National Weather Service Marquette MI
456 AM EDT Fri Sep 22 2017

.SHORT TERM...(This evening through Friday)
Issued at 301 PM EDT THU SEP 21 2017

19Z Visible satellite reveals that patches of fog still linger
over portions of Lake Superior this afternoon, especially eveident
over south central and eastern Lake Superior. Patchy fog/stratus
still lingers over portions of Luce County as well. Elsewhere
across Upper Mi, sunshine and associated mixing have scoured out
any lingering morning fog/stratus.

Tonight, the cold front which stalled out just east and south of the
fcst area this morning is poised to pivot and lift back northward
across the Western Great Lakes later tonight as a warm front. As
this occurs, strong warm air advection and moisture transport will
lift north-northeast across the area bringing back chances for
showers and thunderstorms overnight. Higher dew points with the warm
front combined with nocturnal cooling will also lead to areas of
fog, which could become widespread and possibly dense over southeast
portions of Upper Mi in a developing upslope sse flow. Given the
strong moisture transport and steepening mid-level lapse rates,
upwards of 1500-2000 J/kg should develop mainly over western
portions of Upper Michigan, and extending out across western and
central Lake Superior. While the effective shear is on the marginal
size around 20 knots, enough directional shear looks to be in place
that may sustain updrafts and aid storm organization at times.
Therefore, a few strong to marginally severe storms will be
possible. Given the elevated nature of the convection, hail should
be the primary concern with any stronger cells.

Fri, could see some lingering scattered convection in the morning
mainly over the nw fcst area associated with the warm front and pool
of elevated cape lifting n of the area. If convection does linger
thru Fri morning, pcpn/cloud cover and disruption of sfc wind field
could hold back the rising of temps initially on Fri. However, still
would expect enough sunshine Fri afternoon as warm front lifts north
and core of 925 mb temps near 25c moves overhead that most of the
area should still realize highs in the mid to upper 80s with the
exception of 70s to lower 80s readings downwind of Lake Mi in a
southerly flow.

.LONG TERM...(Saturday through Thursday)
Issued at 455 AM EDT FRI SEP 22 2017

Models suggest that a slowly progressive but amplified pattern
will prevail with a prominent mid/upper level ridge over the Great
Lakes this weekend giving way to troughing by the middle of next
week. Much above normal temps and dewpoints are expected into
Monday with record highs and record high mins likely for many

Saturday into Sunday, even with a strong subsidence inversion under
the 590 DM ridge over the region, forecast mixing to near 850 mb
temps around 20C will support readings in the upper 80s over much of
the area except downwind of Lake Michigan. Adding to the discomfort
will be dewpoints into the mid and upper 60s. Low temps should also
remain in the upper 60s with some downslope locations around 70.
Capping should be strong to minimize shra/tsra chances, per
NAM/ECMWF keeping the pcpn to the north and west. However, the
frontal zone over ne MN into wrn Lake Superior by late Saturday may
allow some shra/tsra into the far west from IWD to CMX by late
Saturday into Saturday evening, per GEM/GFS/GEFS.

Mon-Tue, shra/tsra chances should increase by late Monday into
Monday night as the mid level trough advances into the plains and
the front approaches. The best chance for rain is expected by Tuesday
as a stronger shrtwv and associated low lifts ne near Lake Superior
and drags the front through the area. Although temps will remain
above normal, greater cloud cover will keep max readings mainly in
the 70s Monday and the upper 60s to mid 70s Tuesday.

Wed-Thu, Cooler/drier air should finally take over with breezy wnw
winds behind the front. 850 mb temps dropping to around 1C along
with wrap-around moisture will bring potential for some sct light
showers. Highs will drop back into upper 50s to mid 60s Wed and the
upper 50s by Thursday.

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 130 AM EDT FRI SEP 22 2017

Latest satellite imagery shows stratus/fog moving toward KSAW early
this morning on southeasterly flow. Once it arrives, KSAW to stay
LIFR/IFR until after sunrise when the boundary layer mixes out. Low
clouds and fog also moving up toward KCMX, but KIWD under the
influence of weak downslope flow at this time and thus expect the
fog to hold off there until 9Z or so. LLJ moving into the area will
produce LLWS over the western TAF sites overnight. Shower and
thunderstorm activity has fired over northern MN and this activity
will eventually reach the western U.P., but a few hours later than
earlier expected. Best chances for thunder at KCMX, but confidence
is not high in terms of areal coverage. The fog and low clouds exit
the area shortly after daybreak, with VFR conditions returning for
the remainder of the forecast. There is a slight chance for showers
and thunderstorms over KCMX late in the forecast, but have left out
for now.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 301 PM EDT THU SEP 21 2017

Latest visible satellite still reveals patches of fog over portions
of Lake Superior which could linger into tonight. With lower to mid
60s dewpoints moving across the area and lingering into early next
week, patchy fog could persist for several days across the lake.
Other than a brief increase this evening in winds to 20 to 25 knots
over the western part of the lake, expect winds to generally be
below 20 knots through the early part of next week under a weak pres
gradient. As a warm front lifts north across the area tonight,
scattered thunderstorms will be possible over mainly the western
half of the lake and a few could contain large hail.

Upper Michigan...
Lake Superior...
Lake Michigan...
  Dense Fog Advisory until 11 AM EDT this morning for LMZ221.



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